The prior art has previously suggested the use of an expanding collet secured within an aperture of a workpiece or machine tool for guiding a movable tool. U.S. Pat. No. 1,592,166, inventor, W. H. Turner, and issued July 13, 1926, shows an expanding collet-type bushing for a reamer. U.S. Pat. Nos. 1,729,862; 1,806,891; and 1,963,803 further show expanding bushings or pilots for cutting tools.
U.S. Pat. Nos. 2,020,439 and 3,674,375 disclose the concept of guiding a boring bar at two axially separated places, with the boring tool between. This patent, as well as U.S. Pat. Nos. 2,065,486 and 3,977,805, also discloses the concept of utilizing a type of universal joint so that the axis of the boring tool and the axis of the drive therefor need not be in exact alignment.
Where deep holes are being bored or otherwise machined, it has previously been suggested to utilize four wear strips on a boring tool guide bushing, and this has been disclosed in U.S. Pat. Nos. 2,334,795 and 3,348,434.
U.S. Pat. No. 4,365,917 permits angular adjustment and clamping of a spherical guide bushing by means of air pressure.
In the boring of a deep hole in a workpiece and subsequent machining of an annular surface on that workpiece which is in a plane perpendicular to the boring tool axis of rotation, there is a problem in getting such annular surface perpendicular or normal to such axis during the subsequent machining step. This is part of the general problem of precision machining of surfaces of revolution relative to an axis, whether such surfaces are annular, cylindrical, or conical. As an example, the preferred embodiments emphasize annular surfaces.
The problem is greatly compounded when the boring of the workpiece is attempted through two separate axially separated portions of the workpiece to form two axially separated workpiece apertures. This necessarily means that the workpiece is long and the boring bar is long, and hence may flex or otherwise bore two apertures which are not exactly coaxial. Then with the subsequent machining of the annular surfaces, one each supposedly normal to the axis of the adjacent aperture, these two annular surfaces have been found to be not in parallel planes. An example of where parallel planes are desired on two spaced portions of a workpiece is in the machining of bores in a large valve to achieve two fluid flow apertures and then the machining of two annular surfaces to receive valve seats, with the valve seats supposedly parallel to receive a perpendicularly moving gate valve which is to be received in close and fluidtight communication with the valve seats. If the two valve seats are not parallel, then there will be leakage in the gate valve. The prior art attempts to machine such two annular surfaces necessitated careful boring of the two workpiece apertures and careful reaming or other machining to try to obtain these two apertures coaxial within a minimum tolerance, and hence they were both precision bores.
Next, annular surfaces on the two spaced portions of the workpiece were machined, each normal to the adjacent aperture axis, and hence it was presumed that these two annular machined surfaces were parallel. In a large valve body which might be four or five feet long, this machining could take days to complete.